Technical Field
The present invention relates to a paper transfer device.
Background Arts
A line-type inkjet printer in which printing is done by ejecting inks from fixed inkjet heads onto a paper while transferring the paper is generally known.
Such a line-type inkjet printer is provided with an under-head transfer unit that transfers a paper just under inkjet heads while suctioning the paper onto its transfer surface. With respect to such an under-head transfer unit, a so-called air-suction type is widely known (e.g. see a Patent Document 1: Japanese patent application publication No. 2010-111507).
An air-suction type under-head transfer unit includes a transfer belt on which a lot of through holes are formed, a chamber that forms a negative pressure chamber for generating suction forces through the through holes of the transfer belt, and a fan that exhausts air from the chamber. Negative pressure is generated in the chamber by driving the fan, and thereby air is suctioned through the through holes to generate suction forces at the through holes of the transfer belt. The transfer belt is moved while holding a paper thereon by the suction forces, so that the paper is transferred.
In such an air-suction type under-head transfer unit, a transfer belt is looped over rollers distanced from each other along a transfer direction, and a chamber is disposed beneath the transfer belt and between the rollers. Due to the configuration explained above, there are areas that cannot be covered by suctioning of the chamber at an upstream-side end and a downstream-side end on the transfer belt. Within the areas, air is not suctioned (sufficiently) through the through holes of the transfer belt. Therefore, suction forces become weakened on upstream and downstream sides of the air-suction type under-head transfer unit.
There exists a line-type inkjet printer in which a paper is transferred along a transfer path extending downward from its air-suction type under-head transfer unit. When a leading end of a paper is led to the transfer path extending downward from the under-head transfer unit in such an inkjet printer, an upward force occurs at a trailing end of the paper due to stiffness of the paper. In addition, as explained above, suction forces is weakened on a downstream side of the under-head transfer unit. Therefore, the trailing end of the paper whose leading end is being led to the transfer path extending downward becomes easily uplifted from a transfer surface of the transfer belt.
When the paper is uplifted from the transfer surface, it is concerned that the paper may contact with inkjet heads. If the paper contacts with the inkjet heads, the inkjet heads may be damaged. If a mechanism for pressing the paper such as a roller is provided on the downstream side of the under-head transfer unit in consideration of these concerns, the paper can be prevented from being uplifted.